AuthorTopic: Water Jet Drives & 3D Printing (Read 31005 times)

Quick update from the weekend, I didn't achieve as much as I was hoping to, this is mainly due to a couple of 3D print failures, which meant that the new bow I had planned had a massive chunk missing from the middle, so I am waiting for more filament to arrive and then have another go at printing the largest part for the third time!

I did however have a successful run of the brushed 775 on 3S, it performed well, not getting noticeably hot and cruised at full power pulling around 60A, I would like to do a test in the future on either 5 or 6S to see what the power consumption is like.I had also taken the 1900KV inrunner setup with the 2:1 ratio gearbox and was all ready to run on 6S, when I discovered that, despite bringing a motor coupling this time, it was the incorrect one and meant for a different motor, oh well, next time maybe.

Quick update on how the 3D printed bow extension is going, finally managed to successfully print the centre sections and found some time to assemble everything in the shedshop tonight, hopefully testing down the lake this weekend.

So got the jet boat on the lake today, testing with the new bow extension and running the old 1900KV inrunner on 6S through a 2:1 reduction gearbox giving 21280 RPM.

On the plus side, the boat didn't sink, catch fire or blow anything up... however, although the new bow extension works really well at cutting through surface swell, it throws up one hell of a bow wave and by the end of the run there was over an inch of water inside the hull due to the huge amounts of water flowing over the not so water tight lid, it is a really good thing that the Turnigy ESC I am using is 100% waterproof!Nevermind, that motor, along with the rest of the boat has been to the bottom of the lake before and survived, so I am sure that after a few days drying out on the radiator, all will be well again, wish I could say the same for the gearbox, where there was minor failing of the grubscrews which held the spur gear onto the output shaft, this lead to the drive shaft walking forward, the shaft coupling mining it's way through the 3d printed motor mount and the impeller to mince itself on the inside of the tunnel, again.Unfortunately the brass gears are also a little worse for wear, but this has more to do with the approximate 2240W they had to endure, rather than some dodgy grub screws giving way, this all means the inside of the hull now sparkles with the remnants of the gears and I will be rebuilding the gearbox with something stronger, maybe helical this time.But it is easy to fixate on the negative where as today was an overall success with the prototype tearing across the club lake, it is a real shame that I killed the watt meter on the last outing, but a new year will soon be upon us and I feel the need to break out the proper hulls.

Not been getting much done of lat due to pressures at work, (stupid reality getting in the way of my fun! ) but I have found some time this weekend to sit down and get some work done on the jet boat design, this time building on the success of the 6S 1900Kv inrunner 2:1 gearbox, I am making the following mods:

Good reasons for these changes, new motor, bigger, better and who doesn't like more power?!?! On a more serious note, jetdrive's are phenomenally power hungry devices, the 1900Kv works well, but even with water cooling, it is still very hot at the end of each run, so the thinking is this, bigger motor equals more torque due to increased mechanical advantage, this means more power and more power, leading to a less stressed motor, which means cooler running... well that's the theory.With the new GOOLRC motor having a rating of 2000Kv, I decided to change the gear ratio, as I was changing the gears anyway, dropping the overall RPM will drop the current draw, which means cooler running and longer run times, I have also noticed from the GoPro POV footage that the jet unit sounds very laboured above 85% throttle, I believe this is due to a lack of flow through the unit, due to restrictions in the design, water in / out is not equal to demand, the new design of drive should address these issues.At the moment, with the 1900Kv 6S setup we are getting a drive input speed of: 1900 x 22.4 = 42560 x 0.5 = 21280RPM, now this appears to be a tad fast, as I have found that this unit prefers speeds in the 18 - 19K RPM range, anything more than that suffers badly from the rules of diminishing returns, the new setup will give: 2000 x 22.4 = 44800 x 0.43 = 19264RPM, the parts for the new gearbox are printing as I type, so hopefully I can bolt it together tonight and get down the lake for testing tomorrow.

I also have news of the twin jet unit and some early work in progress screen grabs to share with you guys, as over the festive period I managed to start designing the new and improved unit, bigger, better and more free flowing than the old one, this will be a true 40mm unit, with the impeller OD being 40mm and the tunnel being 42mm ID, I have also redesigned the stator housing, opening it up to drastically improve through flow, the trade off is a slight decrease in flow velocity, but the increase in flow volume should compensate for this.After a thorough inspection of the large fibreglass hull I bought, I have decided it will be less work in the ShedShop to 3D print an entire hull, instead of trying to make the new hull work with what I have, this works for me as I have very little time to physically get out to the ShedShop and do stuff, but my 3D printers can get a huge amount done when I am at work.The new jet design will also come with a range of new and improved reversing nozzles, I have taken the excellent work that Yogibar has done and reworked his drawing to make it work with the larger unit I am designing.

With any luck more updates tomorrow after a morning of tearing it up at the lake!

Good progress, I'm collecting a second machine next week with dual extrudes and a3D scanner.

I was browsing the MHZ website and they do some bigger jet drives which I thinkAre designed for small petrol engines but are worth a look.

When I printed out the main body I was thinking there must be a good reason the the geometry changing at the impeller. I think it's to induce an increase of pressure difference at the inlet by increasing the area which would usually slow the flow but the impeller than accelerates the water. Something I'll have to have a look into a bit more closely.

A successful afternoon down at the lake, the gearbox survived, the new motor runs smoothly, as well as coolly and I appear to have fixed the water ingress issue with some prop shaft grease on the shaft seal, result. The only minor flaw was a recurring electrical issue which is proving a pain to track down and annoyingly intermittent, however, I got some power runs on film, the best footage can be seen here:

I am extremely happy with how the new gearbox / motor combo performed today, the new gears absorbed all of the abuse I threw at them and the prototype now sounds like it is powered by a jet engine, at no point after a run did the motor ever feel hot or even warm to the touch, meaning that it is operating well within it's comfort zone, as well as returning very promising figures from the Watt meter, which I may be able to improve with a bit of tuning on the timing of the ESC, half throttle is around 27 - 30A and flat out is around 93A, a big improvement over the 110A full throttle figure for the 1900Kv motor.

Been super busy recently with work and family celebrations, hence the lack of updates on anything, but I have acquired a new toy recently, not really intentionally, but whilst visiting my parents the other weekend, it came up on eBay, I managed to negotiate a good price and most importantly, it was only a few miles off my route home to collect it, so no worries with couriers damaging the package in transit.So I am now the proud owner of a secondhand Formlabs 1+ SLA printer, sure it doesn't come with some of the fancier features of the Form 2, but it is still a very capable printer, the quality of which is in a different league to what a well setup FDM printer can produce.To put this into perspective, the best I can reliably get out of my Lulzbot mini is a 0.14mm layer height using a 0.5mm diameter nozzle, this naturally places limitations on the resolution you can print at, where as the Formlabs 1+ can print down to a layer height of 0.025mm, combine that with a laser tracing out the parts, (I don't know the spot size of the laser) this produces parts which are seamless in comparison.The photo of an impeller is printed at a layer height of 0.05mm and took around 2.5 hours, it is not very clear in the photos, but you can see layer lines, but they are very minimal and overall the part looks more like it was injection molded than printed, compare this to the FDM prints, which have much more pronounced layer lines, then the comparison in quality is like night and day.I didn't actually buy this printer to produce jet drive impellers, although they are unarguably better quality in every respect and should perform much better than their FDM counterparts, as the surface is so smooth when compared to FDM, this should all but eliminate the effects of rough surface induced cavitation, I actually bought it to produce parts that the FDM machines are not suitable for, small detail parts for example, the Formlabs machine can produce small, intricate parts that, with very little work, are ready to be painted and stuck onto the model, it also opens up a range of alternative materials that were not previously available to me before, custom flexible rubber Stolly tires anyone? Clear resin is also very useful.

So progress has been a little slow of late on the Jet Drive, partly due to the start of a new Club 500 season, my Trent refurb, but mostly due to me gacking a bolt on the jet unit trying to take it apart, non-stainless bolt in a non-stainless nut with no anti-seize, the two were fused together pretty well, in an attempt to remove the bolt I tried drilling it out, but all this did was overheat the 3D printed stator housing and the bolt melted straight through it. Oh well, I had intended to make some improvements to the unit anyway, plus it gave me an excuse to reprint the stator housing with the cooling water outlet not in line with one of the fixing bolts, yeeah, not was of my more genius moments that, improvements made this time around are:

New stator housing with relocated cooling water outlet

Stronger gearbox with jet plate now integral to thrust block

Single output shaft from gearbox to impeller (should give a smoother top end)

Alex.....are there any issues with the mechanical stability of these plastics?....[in metals we consider creep resistance in turbine blades rotating a high RPM and heat].......so is diametrical growth an issue with the rotor of the jet drives?

I have had the PLA impeller up to 22K Rpm with no real issues, on the earlier version it did expand slightly allowing it to spin on the shaft, as it was only a press fit, but since the inclusion of a Brass uj insert to lock the impeller onto the shaft, I have had no such issues.

FDM stands for, "Fused Deposition Modeling" this is where the printer heats up a plastic filament from a spool and lays it onto the print bed in a very precise manner one layer at a time to build up the model, it is essentially a computer controlled glue gun, just a lot more precise.SLA stands for, "Stereolithography" this one is a bit more special, but basically what happens is, photosensitive liquid resin is place in a special tank with a clear bottom, through the bottom of the tank a UV laser traces out each layer, the build plate then separates from the bottom of the tank taking the first layer with it in a, "peal" process, the build plate then resets slightly higher to allow the next layer of the model to be formed by the laser, this building process allows the model to form out of the resin vat.

Finished prepping the jet boat for the lake tomorrow ready to test all of the upgrades I listed in a previous post, below is a link to a quick bench test video of my reworked SLA printed version of Yogibear's design: https://youtu.be/iOFpeOZ-X-8

Much success down at the lake today testing out the new reversing mechanism, it works like a dream, a couple of minor tweaks to be made for the twin jet drive versions, but apart from that I am extremely happy with the results, short video showing maneuvers on the lake: https://youtu.be/Usji9Mtm32E

The rest of the upgrades to the jet drive unit kind of worked, the single shaft design makes the unit really smooth, the SLA impeller withstood the pounding brilliantly, unfortunately, something has gone wrong in the unit which has introduced insane amounts of end float into the equation, I am attempting to do a diagnostic on the unit at the moment, but can't remove the main drive shaft, as soon as I make some progress I will post my findings.

FDM stands for, "Fused Deposition Modeling" this is where the printer heats up a plastic filament from a spool and lays it onto the print bed in a very precise manner one layer at a time to build up the model, it is essentially a computer controlled glue gun, just a lot more precise.SLA stands for, "Stereolithography" this one is a bit more special, but basically what happens is, photosensitive liquid resin is place in a special tank with a clear bottom, through the bottom of the tank a UV laser traces out each layer, the build plate then separates from the bottom of the tank taking the first layer with it in a, "peal" process, the build plate then resets slightly higher to allow the next layer of the model to be formed by the laser, this building process allows the model to form out of the resin vat.

So finally got the gearbox apart to assess the root cause of the failure and it looks to me that this is down to my own stupidity, where I should of bought Stainless Steel rod for the impeller shaft, I accidentally bought Silver Steel bar instead, this means that it rusts really badly, not only this, but I should of realised that pushing a thrust bearing against a 3D printed part would inevitably end badly, the rotating bearing heated up due to it's small size, this melted the PLA just enough to cause it to stick to the bearing race and then that ripped out the centre of the housing, causing it to fuse to the impeller shaft, no wonder I was seeing higher amp draws on this run!

But rest assured I am already on with yet another modification to have the boat up and running this weekend.